I replaced my dead Crane unit with a Pertronix about a year ago. I didnt remember there being any difficulty with determining which Pertronix to get, however there was a lot of confusion about the right ignition coil. You may already know this but if not, it may help. Pertronix talks about 1.5ohm and 3 ohm coils which correspond to 6 volt and 12 volt coils (the 12 volt necessarily has more windings which results in the higher resistance). Depending on what year/model you have, your spitfire may have come originally with either a 6 volt or a 12 volt coil. In addition, it may have been changed by a previous owner so double check. Both coils put out the same voltage out of the ignition wire to the distributor, the difference is the voltage that they need to operate, the amount that should be seen on the + terminal. You may wonder why Triumph would use a 6 volt coil in a 12 volt system and that is because when you are starting, the heavy draw of the starter (and lack of alternator charging) reduces the available voltage below 12 volts. You get a hotter spark to assist with the difficult task of firing the engine by temporarily overloading a 6 volt coil than underloading a 12 volt one. So normally a 12 volt coil gets 12 volts (nominally) ALL the time on its + terminal. The 6 volt gets the full 12 volts when cranking and then only 6 volts (through either a ballast resistor or ballast wire) when running. What does all this have to do with the Pertronix unit? When you install the Pertronix, it will tell you to hook up the red wire at the + terminal of the coil and the black wire at the - terminal. It will also tell you that you need a 3.0 ohm coil, e.g. 12 volts. No one that Ive spoken with is really sure, but it appears that Pertronix is saying that their unit needs a constant 12 volts to operate. The coil is a convenient place to take it from even though youre really just using a common junction, theres nothing magical about the 12 volts at the coil as compared with anywhere else (although you do want it to be switched in synch with the ignition). And I cant think of anything special about the terminal, the Pertronix is just grounding the coil so it produces a spark and I dont see how the unit could care whether the coil is 3 ohms or 1.5. So what I did was leave the 6 volt coil in place and take a 12 volt source for the red wire from the Pertronix from the remnants of the factory electronic ignition. So far thats worked. Ive also heard that some folks have just run the Pertronix on 6 volts and it seems to work but whether it shortens its life, who can say? So bottom line:
If you have a 12 volt coil and no ballast wire, you are good to go. If you have a 6 volt coil and a ballast wire, you can - Bypass the ballast and replace the coil with a 12 volt (lose advantage of hotter spark when starting) - Keep the 6 volt and find another 12 volt ignition source for the Pertronix (not recommended by them but seems to work) - Keep the 6 volt, hook up to 6 volts and see if it actually makes a difference (uncharted waters). I hope this helps. Good luck with it! Greg Rowe > From: d...@ranteer.com > To: spitfires@autox.team.net > Date: Tue, 14 Jan 2014 16:56:34 -0600 > Subject: [Spits] pertronix > > hi. have a 75 spit; was converted to allison ignition which is pretty dead. > I want to order a pertronix, but it appears there are numerous choices. > > how do I choose???? _______________________________________________ Spitfires@autox.team.net Donate: http://www.team.net/donate.html Suggested annual donation $11.47 Archive: http://www.team.net/archive Forums: http://www.team.net/forums Unsubscribe/Manage: http://autox.team.net/mailman/options/spitfires/arch...@jab.org